Choosing the coarse, medium and fine grained sandstone as study object, the surface topography of the polished rock surface was tested by the white light interferometry optical interferometer, and was characterized with roughness and grain size. The mineral composition and pore structure of the samples were measured also. Under the condition of the mineral content of rock samples basically being the same, the relationship between pore structure and surface grain size was analyzed. The experimental results show that: polishing has an effect on Ra, Rc and Rq, and has little effect on Rv and Rp;polishing has an effect on the average height of specimen surface, but has little effect on the grain diameter of the surface;there is a positive correlation between porosity and the grain size.